Process for the utilization of the exhausted gases from an ethylene oxide synthesis reactor

ABSTRACT

A PROCESS FOR RECOVERING BOTH MECHANICAL ENERGY AND THERMAL ENERGY FROM THE EXHAUST GASES OF AN ETHYLENE OXIDE SYNTHESIS REACTOR. THE EXHAUST GASES ARE PASSED IN HEAT EXCHANGE RELATIONSHIP WITH BOILER FLUE GASES WHICH ARE USED TO DRIVE A GAS TURBINE WHICH IS COUPLED TO THE DRIVE SHAFT OF AN AIR COMPRESSOR. THE EXHAUST GASES DISCHARGING FROM THE TURBINE ARE THEN BURNED IN THE STEAM BOILER. STEAM GENERATED IN THE BOILER IS USED TO DRIVE A STREAM TURBINE WHICH IS ALSO COUPLED TO THE DRIVE SHAFT OF THE AIR COMPRESSOR.

- Jan. 5, 1971 PARMEGMN] ET AL 3,552,122

PROCESS FOR THE UTILIZATION OF THE EXHAUSTED GASES FROM AN ETHYLENE OXIDE SYNTHESIS REACTOR Filed Aug. 6, 1968 g TEMPERATURE CONTROL DEVICE l 2' i I n L. ..J

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United States Patent 3,552,122 PROCESS FOR THE UTILIZATION OF THE EX- HAUSTED GASES FROM AN ETHYLENE OXIDE SYNTHESIS REACTOR Mario Parmegiani, San Donato Milanese, and Oreste Bellofatto, Milan, Italy, assignors to Snam Progetti S.p.A., Milan, Italy, a company of Italy Filed Aug. 6, 1968, Ser. No. 750,644 Claims priority, application Italy, Aug. 8, 1967, 19,320/ 67 Int. Cl. F02c 7/02 US. Cl. 6039.18 1 Claim ABSTRACT OF THE DISCLOSURE A process for recovering both mechanical energy and thermal energy from the exhaust gases of an ethylene oxide synthesis reactor. The exhaust gases are passed in heat exchange relationship with boiler flue gases which are used to drive a gas turbine which is coupled to the drive shaft of an air compressor. The exhaust gases discharging from the turbine are then bumed in the steam boiler. Steam generated in the boiler is used to drive a steam turbine which is also coupled to the drive shaft of the air compressor.

This invention relates to improvements applied to the recovering of the energy content of the exhaust gases flowing from the synthesis reactor of the ethylene oxide.

In a related application (Parmegiani et al., Ser No. 706,139, filed Feb. 16, 1968) there is described a process for recovering thermal and mechanical energy of the exhaust gases of the ethylene oxide synthesis process, by means of combustion at controlled temperature and pressure of the ethylene therein contained and by transferring the high pressure and high temperature gases for the recovery of the mechanical energy, into a turbine coupled directly with the compressor feeding the air of the process.

Now it has been found that it is possible to recover the energy of said exhaust gases in an alternative way to that described in the related application referred to above.

According to the present invention the energy recovery of the exhaust gases obtained by means of the production of the ethylene oxide occurs substantially in two phases in the first of which mechanical energy is recovered by expansion while in the second one thermal energy contained in the expanded gases is recovered for combustion of ethylene and the energy recovery is carried out by means of steam production.

For a better understanding of the present invention reference is made to the accompanying drawing:

1 is the feeding inlet of the exhaust gases containing ethylene, coming from the plant of the ethylene oxide production (not shown in the drawing) which is preheated in the heat exchanger 2, then it is expanded in the turbine 3 coupled with compressors 4 and 4 respectively at low and high pressure, which supply the compressed air required by the process.

The gases coming out from the turbine at lower temperature and high pressure feed one or more burners 5 which auxiliary fuel is also admitted into, which may be not valuable one (heavy fuel oil) with the purpose to produce steam for combustion of ethylene and of the auxiliary fuel in the boiler 6 said steam being overheated in the coil 7 feeding turbine 8 which is also coupled with the above mentioned compressors 4 and 4'.

The gas temperature at the heat exchanger outlet 2 is regulated by means of a device 9 situated upon one of the boiler outlets through which burnt gases are coming out.

The temperature stabilization is achieved by regulating the letting in of the auxiliary fuel into the boiler burner.

Patented Jan. 5, 1971 'ice A typical ethylene producing apparatus in which the invention has application is shown in the accompanying drawing. The reactor 11 for ethylene oxide production is arranged to receive ethylene from an ethylene feeding line 10. The output of the ethylene oxide reactor 11 is delivered to a separator 13 which passes ethylene oxide through output line 12 and delivers the unreacted ethylene to line 1 of the energy recovering apparatus. A water line 14 is arranged to supply water to the separator 13.

In the drawing, the unbroken line shows the steam path, the line with dashes and points shows exhaust gases path from the ethylene oxide synthesis reactor, the line with alternated short and long dashes shows the process air path and finally the line with equal dashes shows the water path.

As far as the operative conditions are concerned the exhaust gas of ethylene oxide synthesis reactor are at a pressure of from 15 to 25 atmospheres and at a temperature of from 10 to 50 0; they are preheated in the heat exchanger 2 at a temperature of from 350 to 460 0., namely lower than the explosion limit of the air-ethylene mixture.

The steam obtained in the boiler may be either envoyed, as above described into a steam turbine to recover from it mechanical energy or may be utilized for different purposes.

The auxiliary fuel may be of various kind and may be utilized also a heavy fuel oil since the combustion products are not directly utilized in a turbine but after that the transferring heat in the heat exchanger 2 occurs said burnt gases are blown oif to the atmosphere.

The advantages of this process compared with those of the main patent are the following ones:

the possibility to use any auxiliary fuel;

the centralized production by combining together the overheated steam produced 'by other heat generators existing in the unit.

What we claim is:

1. A process for recovering energy from the exhaust gases generated in a process for synthesizing ethylene oxide by catalytic oxidation of ethylene with air for use within said ethylene oxide synthesizing process comprising the steps of:

heating said exhaust gases by the passage thereof in heat exchange relationship with the products of combustion from a steam boiler;

driving a gas turbine coupled to an air compressor with said heated exhaust gases;

delivering said exhaust gases from said gas turbine outlet to the burners of said steam boiler for combustion therein;

delivering steam generated in the boiler to a steam turbine coupled with said gas turbine to drive said air compressor; and

delivering the compressed air from said air compressor to the ethylene oxide producer.

References Cited UNITED STATES PATENTS 2,592,749 4/1952 Sedille et a1 6039.12 2,675,672 4/1954 Schorner 6039.18BX 2,718,755 9/1955 Heller 6039.18 3,077,073 2/1963 Kuhrt 6036 3,280,551 10/1966 Bracken et al 60-3902 MARK NEWMAN, Primary Examiner U.S. Cl. X.R. 

